In the polyurethane field, increased interest is being shown in compounds which can be added to the polyurethane polymers to act as fire retardant agents. One such group of reactive flame retardants are the polyalkylene glycol phosphites such as those described in U.S. Pat. No. 3,009,939. However these materials, due to their high OH numbers and crosslinking tendency, are unsuitable for use in flexible urethane foams. In U.S. Pat. Nos. 3,081,331 and 3,142,651, there is disclosed a method of forming polyalkylene glycol polyphosphites having up to 10 phosphite groups in the polymer chain by reacting a trialkyl phosphite with a polypropylene glycol in a molar ratio of 2.1 to 2.5 moles of glycol per mole of phosphite. These materials are also unsuitable for use in flexible urethane foams as a result of their high OH numbers and their tendency to crosslink.
Another attempt at employing reactive flame retardants, described in U.S. Pat. Nos. 3,142,651 and 3,092,651, involves the use of polypropylene glycol poly-hydrogenphosphonates produced by a thermal polymerization. Likewise, polyalkylene glycol hydrogen polyphosphonates have also been produced by transesterifying a secondary hydrogen phosphonate with a polyalkylene glycol according to the procedure outlined in British Pat. Nos. 796,446 and 1,011,118. However, many of these materials have relatively high acidity, causing them to react with and thereby deactivate certain catalyst systems generally used in the formation of polyurethane polymers such, for example, as tertiary amine compounds. The first method has the additional drawback of contamination of the product by the alkylene glycol byproduct, which contamination is not easily removed.
In order to increase the flame retardancy of some of the above described phosphorus compounds, which have low phosphorus content, the prior art has attempted to incorporate various halogen containing substituents into the above described molecules. Thus, U.S. Pat. No. 3,159,605 describes the reaction of halogenated methanes with these compounds. However, these materials like their precursors, have many drawbacks. In particular these products have high OH numbers and low phosphorus content thereby rendering them unsuitable as flame retardants in flexible urethane foams.
It is an object of the present invention to prepare novel polyalkylene glycol alkyl polyphosphites which are suitable as flame retardants for urethane foams, and particularly flexible urethane foams.
It is another object of the present invention, to produce polyalkylene glycol alkyl polyphosphites which have relatively low OH numbers and acidity, high phosphorus content and little if any crosslinking tendency when compared to those flame retardants described in the prior art.
Still a further object of the present invention is to produce mixed phosphite-phosphonate polymer flame retardants containing both alkyl phosphite and haloalkyl phosphonate linkages. These phosphite-phosphonate polymer flame retardants have OH numbers of less than one.
Still other objects will become apparent from the detailed description given hereinafter.